METHOD FOR PERFORMING A TESTING PROCEDURE OF AN ELECTRICAL POWER SYSTEM FOR A WIND TURBINE AND AN ELECTRICAL POWER SYSTEM

Abstract

 The invention is related to a method for performing a testing procedure of an electrical power system (100) for a wind turbine by means of a power supply unit (180), wherein the method comprises connecting the power supply unit (180) to a low voltage distribution system (110) of the wind turbine. Method further comprises closing a low voltage circuit breaker (112) so that electrical connection is provided between the low voltage distribution system and an auxiliary transformer (140) and providing electrical power to a power converter (160) from the power supply (180) unit via the low voltage distribution system (110) thereby energizing a direct current link (162) of the power converter (160). Further on, the power converter (160) is synchronized with an electrical grid (170), and a main transformer switchgear unit (130) is closed, such that electrical connection is provided between a main transformer (120) and the electrical grid (170).

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method and an arrangement for performing a testing procedure of an electrical power system for a wind turbine.

BACKGROUND OF THE INVENTION

[0002] A wind turbine may comprise electrical power system that includes a generator, a main transformer, a main transformer switchgear unit, an auxiliary transformer, an auxiliary transformer switchgear unit, a low voltage distribution system, a power converter and an electrical grid. The electrical grid may also be referred to as wind turbine internal high voltage grid or switchgear bus, different from an external electrical network frequently called grid or public grid.

[0003] The electrical grid may consist of electrical cables connecting the components of the electrical power system. The power converter may include a direct current link.

[0004] Before a wind turbine is connected to an external electrical network for providing electrical power to consumers, the electrical power system of the wind turbine needs to be commissioned.

[0005] Components of the electrical power system of the wind turbine need to operate according to the requirements and standards. A high voltage source is needed to test high voltage components of the electrical power system of the wind turbine that may comprise the main transformer, the auxiliary transformer, and/or high voltage cables. High voltage needed for testing of the electrical power system of a wind turbine may, for example, be provided by means of external hardware components at a test area. Alternatively, wind turbine components may be transported to a location where a high voltage connection point is available for performing the test, before transporting the wind turbine components to the final site of erection of the wind turbine.

[0006] One way of performing testing procedure of the electrical power system for the wind turbine includes either providing expensive hardware components capable of generating high voltage to the test area or transporting pre-assembled wind turbine components to a location where such high voltage connection point exists. Some of the drawbacks of these methods are price of hardware components capable of generating high voltage, transportation costs, time duration needed for contracting and developing high voltage connection point.

SUMMARY OF THE INVENTION

[0007] It is the object of present invention to offer alternative method for performing testing procedure of an electrical power system, preferably for a wind turbine.

[0008] This objective is achieved by the independent claims. The dependent claims describe advantageous developments and modifications of the invention.

[0009] In accordance with the invention a method for performing a testing procedure of the electrical power system is provided, preferably for the wind turbine. A power supply unit is electrically connected to a low voltage distribution system of the wind turbine. A low voltage circuit breaker is closed thereby providing electrical connection between the low voltage distribution system and an auxiliary transformer of the wind turbine. Electrical power is provided to a power converter from the power supply unit via the low voltage distribution system thereby energizing a direct current link of the power converter. The power converter is synchronised with an electrical grid. A main transformer switchgear unit is closed such that electrical connection is provided between a main transformer and the electrical grid.

[0010] Advantage that described method offers, is that commissioning of electrical power system can be performed by generating high voltage without the necessity of using additional high voltage generating hardware, and/or without the necessity to transport components of the electrical power system to a testing facility that offers a high voltage connection point. Instead, performing the testing procedure can be executed in the original assembly workshop.

[0011] The term "main transformer" defines the transformer that can be in a main power path between the generator and an external electrical grid.

[0012] The term "auxiliary transformer" defines the transformer that can be located between the low voltage distribution system and the main transformer. It can be used to adapt the main transformer output voltage to a voltage level of auxiliary power system during regular operation of the wind turbine. According to the invention, auxiliary transformer can be used as a step-up transformer.

[0013] According to a preferred embodiment of the invention the power supply unit that is connected to the low voltage distribution system may be a 3-phase alternating current power supply unit, preferably a low voltage 3-phase alternating current power supply unit. This type of the power supply unit may be available at any testing facility for electrical power system, preferably for a wind turbine.

[0014] In a further embodiment, before the power supply unit is connected to the low voltage distribution system of the wind turbine, the power converter may be switched off. Alternatively, a direct current link of the power converter may not be energised.

[0015] In an embodiment the power converter may be comprised of a single power converter module. Alternatively, the power converter may comprise two or more power converter modules operating in parallel.

[0016] In an exemplary embodiment energising the direct current link of the power converter may be performed by providing direct current to the direct current link of the power converter via a direct current pre-charging unit.

[0017] As one option, the direct current pre-charging unit may be adapted to convert alternating current from the low voltage distribution system to direct current for providing energy to the direct current link of the power converter.

[0018] Synchronization of the power converter and the electrical grid can be achieved by a converter control unit controlling a grid side converter so that the phase and frequency of the grid side converter output voltage match the phase and frequency of the electrical grid voltage.

[0019] In an embodiment the main transformer may be a three-winding transformer with two windings connected to outputs of two power converter modules. Alternatively, one of the main transformer windings may be connected to output of one power converter module.

[0020] The electrical grid may be an internal high voltage grid of the wind turbine.

[0021] The invention is further directed to an electrical power system for which the previously explained method is performed. The electrical power system comprises a low voltage distribution system, a power supply unit, a main transformer, a main transformer switchgear unit, an auxiliary transformer, an auxiliary transformer switchgear unit, a power converter and an electrical grid.

[0022] The electrical power system may further comprise a distribution panel, a cooling system, a fire protection system, a direct current pre-charging unit, a control device, and electrical cables.

[0023] The direct current pre-charging unit may be electrically connected with the low voltage distribution system of the wind turbine.

[0024] Advantageously, the direct current pre-charging unit may be adapted to convert alternating current from the low voltage distribution system to direct current for providing energy to the direct current link of the power converter.

[0025] As a preferred embodiment the power supply unit may be integrated in a test bed or a workshop.

[0026] It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this application.

[0027] The invention is also applicable for any type of electrical power systems used, e.g. in power generating facilities or other industrial facilities.

[0028] The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the invention will now be described, by way of example only, with reference to the drawings.

FIG. 1:

shows schematically an embodiment of an electrical power system for a wind turbine according to the invention in a principle manner;

FIG. 2:

shows a second embodiment of an electrical power system for a wind turbine according to the invention in a principle manner;

FIG. 3:

shows an embodiment of an electrical power system for a wind turbine with illustrated energizing flow of components of the electrical power system while performing the method according to preferred embodiment.

[0030] The illustration in the drawing is schematical. It is noted that for similar or identical elements in different figures, the same reference signs will be used.

[0031] Some of the features and especially the advantages will be explained for an electrical power system for a wind turbine, but obviously the features can be applied also to the electrical power systems of other power generating plants or industrial facilities.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Referring now to FIG. 1, an electrical power system 100 for a wind turbine is illustrated.

[0033] The electrical power system 100 includes a low voltage distribution system 110, a main transformer 120, a main transformer switchgear unit 130, an auxiliary transformer 140, an auxiliary transformer switchgear unit 150, a power converter 160 and an electrical grid 170. Voltage level of the low voltage distribution system 110 may be for example 400 volts. The low voltage distribution system 110 may be used to deliver electrical energy to components of an auxiliary system 200 of a wind turbine. These components may include control devices, sensors, cooling system, fans, pumps, heaters, air treatment units and/or lights.

[0034] A first low voltage circuit breaker 111, when closed, provides electrical connection between the low voltage distribution system 110 and a power supply unit 180. Electrical connection between the low voltage distribution system 110 and the power supply unit 180 is disrupted when the first low voltage circuit breaker 111 is open.

[0035] In a preferred embodiment, the power supply unit 180 is a 3-phase alternating current low voltage power supply unit. The low voltage power supply unit may be, for example, a 400 volts 3 phase power supply unit. In general, the low voltage power supply unit and the voltage level of the low voltage distribution system 110, in accordance with the invention may be in a range of 100 volts to 2000 volts, preferably in the range 200 volts to 600 volts.

[0036] The power supply unit 180 may be comprised within the electrical power system 100 for a wind turbine. Alternatively, the power supply unit 180 may be integrated in a test bed or in a workshop at a location where the electrical power system 100 could be tested.

[0037] A second low voltage circuit breaker 112 allows electrical connection between the low voltage distribution system 110 and an auxiliary transformer 140.

[0038] The auxiliary transformer 140, in a preferred embodiment, is used to raise the voltage from the voltage level of the low voltage distribution system 110 to the high voltage level of the electrical grid 170. As an example, the auxiliary transformer 140 may be used to raise voltage from the voltage level of 400 volts to the voltage level of 20 kilovolts.

[0039] The auxiliary transformer 140 can be electrically connected to the main transformer 120 via an electrical grid 170. The auxiliary transformer 140 is equipped with an auxiliary transformer switchgear unit 150 and the main transformer 120 is equipped with the main transformer switchgear unit 130.

[0040] The main transformer switchgear unit 130 and the auxiliary transformer switchgear unit 150 are used to either electrically connect or disconnect respective transformers from the electrical grid 170.

[0041] The power converter 160 is connected to the electrical grid 170 via the main transformer 120. The power converter 160 may be comprised of a generator side converter 161, a direct current link 162 of the power converter 160 and a grid side converter 163. Switching operation of the power converter 160 is controlled via a converter control unit 164. The power converter 160 may be comprised of multiple power converter units operating in parallel, for example two units as shown in figure 2. The power converter 160, as shown in figure 2, may comprise two generator side converters 161a and 161b, two direct current links 162a and 162b of the power converter 160 and two grid side converters 163a and 163b.

[0042] The direct current link 162 of the power converter 160 may be electrically connected to the low voltage distribution system 110 via a direct current pre-charging unit 165.

[0043] The main transformer 120 may be a three-winding transformer where two windings are connected to outputs of different converter units, as shown in figure 2.

[0044] Method for performing a testing procedure of the previously defined electrical power system 100 for a wind turbine is described next.

[0045] First, the low voltage circuit breaker 111 is closed and the power supply unit 180 is connected to the low voltage distribution system 110. Power supply unit 180 is thereby powering the low voltage distribution system 110. This flow of energizing the low voltage distribution system 110 from the power supply 180 is illustrated in figure 3.

[0046] In the following, the low voltage circuit breaker 112 is closed such that electrical connection is provided between the low voltage distribution system 110 and the auxiliary transformer 140. In this way, the power supply unit 180 is supplying the auxiliary transformer 140 with electrical power. This flow of energizing the auxiliary transformer 140 with electrical power from the power supply 180 is illustrated in figure 3. In a preferred embodiment, the power supply unit 180 is a 3 phase, 400 volts, alternating current power supply unit. The auxiliary transformer 140 raises the voltage from the voltage level of the power supply unit 180 to a high voltage level, preferably to that high voltage level that would be used on the electrical grid 170 in the normal mode of operation of the electrical power system 100. In a preferred embodiment, high voltage level on the auxiliary transformer 140 is 20 kilovolts. In general, a high voltage provided by the auxiliary transformer 140 in accordance with the invention may be in a range of 5 kilovolts to 40 kilovolts, preferably in the range 10 kilovolts to 30 kilovolts.

[0047] The auxiliary transformer switchgear unit 150 is closed and the high voltage is provided to the electrical grid 170.

[0048] Actuation of all mentioned switchgear units and circuit breakers may be executed by means of Programmable Logic Controller (PLC) or Digital Signal Processor (DSP) or any suitable signal processing unit.

[0049] The electrical grid 170 may also be referred to as internal high voltage grid or switchgear bus. The electrical grid 170 may be connected to and/or disconnected from the external electrical grid by actuating grid connection switchgear 171.

[0050] As a further step, the power converter 160 is charged by means of the power supply unit 180. Electrical energy is provided, via the low voltage distribution system 110 to the direct current link 162 of the power converter 160. This flow of energizing the direct current link 162 of the power converter 160 from the power supply 180 is illustrated in figure 3.

[0051] The direct current link 162 of the power converter 160 may comprise a capacitor and/or an inductor capable for storing and releasing electrical energy (not shown in the figure). For transforming alternative current from the power supply unit 180 to direct current required for charging of the direct current link 162 of the power converter 160, the direct current pre-charging unit 165 may be used.

[0052] The direct current pre-charging unit 165 may comprise at least one rectifier and/or inverter.

[0053] Output of the power converter 160 is synchronised with the electrical grid 170. Converter control unit 164 controls the grid side converter 163 so that the phase and frequency of the grid side converter 163 output voltage match - are synchronous to - the phase and frequency of the electrical grid 170 voltage.

[0054] Once the power converter 160 output voltage is synchronised to the voltage of the electrical grid 170, main transformer switchgear unit 130 is closed, and electrical coupling is provided between the main transformer 120 and the electrical grid 170. This energization flow is illustrated in figure 3.

[0055] In this way all components of the electrical power system 100 will be provided - loaded - with their rated voltage. Once the components are loaded with their rated voltage, it is possible to perform inspection of the various electrical components of the electrical power system 100. Inspection may comprise visual inspection of various switchgear units, cables and terminals. Alternatively, inspection may comprise performing electrical test procedures.

[0056] High voltage required for energizing of the components connected to the electrical grid 170 is provided by means of the power supply unit 180. This method is advantageous compared to alternative ways of energizing high voltage components of the electrical power system 100 as no further external hardware is needed. Alternative ways of providing high voltage to the electrical grid 170 may include connecting the electrical grid 170 to external hardware equipment capable of providing matching high voltage to the electrical grid 170 of the electrical power system 100. Alternatively, assembled wind turbine comprising electrical power system 100 may be transported to a location where high voltage connection point is provided. Both alternative methods are particularly difficult to implement if the wind turbine comprising the electrical power system 100 is located offshore or in other locations distant from testing laboratories, for example at the final site or at an area of assembly, both onshore or offshore.

Claims

1. Method for performing a testing procedure of an electrical power system (100) for a wind turbine by means of a power supply unit (180), wherein the method comprises:

- connecting the power supply unit (180) to a low voltage distribution system (110) of the wind turbine,

- closing a low voltage circuit breaker (112) so that electrical connection is provided between the low voltage distribution system and an auxiliary transformer (140),

- providing electrical power to a power converter (160) from the power supply (180) unit via the low voltage distribution system (110) thereby energizing a direct current link (162) of the power converter (160),

- synchronizing the power converter (160) with an electrical grid (170), and

- closing a main transformer switchgear unit (130) such that electrical connection is provided between a main transformer (120) and the electrical grid (170).

2. Method according to one of the preceding claims, characterised in that the power supply unit (180) is a 3-phase alternating current power supply unit, preferably a 3-phase alternating current low voltage power supply.

3. Method according to one of the preceding claims, characterised in that the power converter (160) is switched off before connecting the power supply unit (180) to the low voltage distribution system (110) of the wind turbine.

4. Method according to one of the preceding claims, characterised in that the power converter (160) is comprised of at least two power converter units operating in parallel.

5. Method according to one of the preceding claims, characterised in that energizing the direct current link (162) of the power converter (160) is performed by providing direct current to the direct current link (162) of the power converter (160) via a direct current pre-charging unit (165).

6. Method according to claim 4,
characterised in that the direct current pre-charging unit (165) is adapted to convert alternating current from the low voltage distribution system (110) to direct current for providing energy to the direct current link (162) of the power converter (160).

7. Method according to preceding claims,
characterised in that the synchronization of the power converter (160) and the electrical grid (170) is achieved by a converter control unit (164) controlling a grid side converter (163) so that phase and frequency of the grid side converter output voltage match the phase and frequency of an electrical grid voltage.

8. Method according to one of the preceding claims, characterised in that the main transformer (120) is a three-winding transformer with two windings connected to outputs of two power converter modules.

9. Method according to one of the preceding claims, characterised in that the electrical grid (170) is an internal high voltage grid of the wind turbine.

10. Electrical power system (100) characterised in that the electrical power system (100) comprises a low voltage distribution system (110), a power supply unit (180), a main transformer (120), a main transformer switchgear unit (130), an auxiliary transformer (140), an auxiliary transformer switchgear unit (150), a power converter (160) and an electrical grid (170),
wherein the electrical power system (100) is configured to execute the method according to any of the claims 1 to 9.

11. Electrical power system (100) according to claim 10 characterised in that the electrical power system (100) further comprises a distribution panel, a cooling system, a fire protection system, a direct current pre-charging unit (165), a control device, and electrical cables.

12. Electrical power system (100) according to claim 11, characterised in that the direct current pre-charging unit (165) is electrically connected with the low voltage distribution system (110) of the wind turbine.

13. Electrical power system (100) according to the claims 11 or 12 characterised in that the direct current pre-charging unit (165) is adapted to convert alternating current from the low voltage distribution system to direct current for providing energy to a direct current link (162) of the power converter (160).

14. Electrical power system (100) according to any of the preceding claims, characterised in that the power supply unit (180) is integrated in a test bed or a workshop.

Drawing